ONYX

BERLIN IRON

Berlin iron is made from cast iron and delicate wire pieces. For more information, see here.

Germany, Cast iron earrings. c. 1820-1830 V&A Museum

ENAMEL

Enamelis fired ground glass. In theory, almost all methods of enamelling can produce black items but generally it is en grisaille, niello and taille d’epargne which are known for being worked in black. (Technically, niello work is not true enamel but is usually classified as such)

GUTTA PERCHA

Gutta Percha is a type of rubber derived from the gum of Asian trees. It is usually molded rather than carved and mould lines can be visible when examined carefully. When rubbed vigorously, it gives off an acrid, rubber smell. It is very flexible and durable and can produce a wide variety of jewellery items. Upon close inspection, you can see that it is actually brownish-black. Popular through the mid and late Victorian era, it made its debut at the Great Exhibition of 1851.

Gutta Percha Brooch.

VULCANITE

Vulcanite is vulcanised India rubber formed using sulphur. It was first patented in 1844 by Charles Goodyear. Vulcanite is almost always moulded, as opposed to carved. It is actually white and can be dyed to produce a variety of colours, often in imitation of coral and tortoiseshell. Most commonly, however, it was dyed black and used in mourning jewellery as a substitute for jet. Over time, black vulcanite usually turns dark brown. It is lightweight and warm to the touch. It will develop a sheen with polishing but is never as glossy as jet. Like jet, it will leave a brown streak on porcelain or unglazed tile.

Victorian Vulcanite cameo pendant.

FRENCH JET

French jetis black or very dark red glass. It can sometimes bebacked with foil or attached to a metal setting but is most commonly found as beaded necklaces. It first made its appearance in the early part of the 19th century but came into its own in the 1860s when the techniques to produce it were perfected. It was produced in France, Germany, Austria, England and what is now the Czech Republic. It is cold to the touch and heavier than jet and has a distinctive glitter. Sometimes it is roughly moulded or carved to further simulate jet. Upon close examination, it can often be identified by tiny chips. If you gently tap it against your teeth, you should be able to identify the chink as glass.

French jet necklaces. Elder and Bloom.

BOG OAK

Like jet, bog oak is fossilised wood. It is usually mined from the bogs of Ireland and is not necessarily oak but can be fir, yew or pine. Similar in feel to jet, it is lightweight and warm to the touch but generally has a more matte finish. It was used from the early 1800s and grew in popularity after 1852 when techniques involving heat and pressure were invented to mold it and create detail. It can be carved or moulded. It is generally found in mourning jewellery as a substitute for jet but can also often be found with Irish motifs in the form of souvenir jewellery.

Victorian bog oak brooch.

TORTOISESHELL

With age, tortoiseshell can darken enough to appear black. See here and here.

Many pieces of antique gold jewellery (particularly from the Georgian era or pieces which are handcrafted) are unmarked and therefore gold testing is necessary. This article is a practical guide to using an electronic gold tester made by TRI electronics (I personally have the GXL-18 model.).

This is my decimation of the information in the TRI Electronics user manual which I hope makes a good quick reference for those interested. HOWEVER – PLEASE ALWAYS REFER TO THE MANUFACTURERS INSTRUCTIONS FOR THE FINAL SAY ON HOW TO USE THESE TESTERS.

OPERATION PROCEDURE

The procedure for testing can be shortened to the following easy to remember four words:

LOAD – CONNECT- SELECT- TEST

For more details, see below:

1) Load the polyethylene gel tube in accordance with the manufacturers instructions.

2) Connect the following:

a) The black wire to the sensor’s plug outlet.

b) The black and red wire connector to the display unit.

c) The red wire to the testing plate.

3) Turn the unit ON. The unit should now read ‘G-XL-18 READY TO TEST…’

4) Selecting a point to test:

a) Make sure the point to test is close to BUT NEVER TOUCHING the alligator clip.

b) Do not allow the gel to touch the alligator clip as this will corrode it.

c) Thoroughly clean the testing point with the eraser.

5) The First Part of the Test

Place a tissue, paper towel or rag under the tip of the sensor.

Hold the sensor in a vertical position with the nozzle down.

Twist the Rotary Cap counter clockwise, one click at a time, until a drop of gel appears.

Wipe this first drop of gel away.

Turn again (usually one or two clicks) until more gel appears.

Touch the sensor to the selected area of the test object.

6) Select a gold colour button.

Depending on the visible colour of the metal you are testing, select one of the following buttons on the unit (see manual for diagram of button locations):

Y-Yellow

W-White

R-Red

G-Green

7) Keep the sensor in a vertical position for about 5 seconds. This is is when the gold value is calibrated.

8) The karat value and European Standard are displayed on the instrument. (Tip: Write this down with a pen and paper you keep to hand, along with your reference for the item).

9) Turn off the instrument.

POINTS TO KEEP IN MIND

1) Electronic tests are not infallible. If you achieve a result which is outside of expectations then retest in a different location after cleaning your equipment and your item and use new gel. Keep testing until you get a consistent result. Always make a note for the customer if you are selling gold items tested with an electronic tester explain that the test is not infallible and should be seen as a guide only.

2) Be careful with fine chains. Very fine chains can be crushed by the dispenser. Avoid pressure with fine gold chains whilst keeping gel contact. It’s recommended to get the results of two or three tests.

3) Be aware of air bubbles. Sometimes air bubbles with give a high or low reading. Always retest and apply common sense to the results of your readings.

4) Clean Tip. A clean tip is essential for an accurate reading.

a) If you are not using the gold tester more than once a week it is advised that you remove the gel tube from the sensor and store it to keep the gel from drying out.

b) Before replacing the gel, whether with a new tube or with one previously removed, clean thoroughly with SC-10 Cleaner Kit.

c) If the tester has not been used for over a week, clean the tip with the plastic cleaner provided by inserting the tip into the nozzle of the sensor.

d) If gel drops are not dispensed by rotating the twist cap, clean the sensor with the SC-10 Cleaner Kit.

5) Solder areas and heavy castings with unevenly dispersed metal can give false readings. Always retest in different areas of the piece.

6) Italian Gold may be waxed and can give a false reading. If you suspect the metal may be waxed, clean the testing area with heavy erasing or with nitric acid (only a drop is required).

7) Skin oils can give a false reading. In heavily worn pieces clean the testing area first with the eraser or with non-acetone nail polish remover.

8) Plated Gold. Usually a tiny scratch or a pin prick will allow gel penetration to the base material on plated pieces. If this is not sufficient, two or three tests are recommended with a thorough eraser cleaning in between. If the item is gold plated, the karatage will decrease with each testing. A solid gold piece will not decrease with each test.

9) Dispose of the drop of gel following each test.

10) Use every other gel drop for best results.

11) DO NOT LET GEL OR SENSOR NOZZLE TOUCH THE ALLIGATOR CLIP!

12) When removing the cable from the sensor, do not pull the wire! Pull the plug itself to avoid damage.

13) Testing objects larger than the Alligator Clip. In this instance, unhook the red wire from the testing plate and proceed with the test as per instructions but with the tip of the red wire touching the object.

14) Do not retest the same spot without eraser cleaning.

15) Refer to the manual for full care and maintenance of the tester and follow their recommendations.

TROUBLE SHOOTING

1) Problem: Brown spot on test surfaces

Solution: Rub the spot with eraser

2) Problem: Display unit reads “NOT GOLD”

Solution: Check the wire contacts and the connections

3) Problem: Display has no reading

Solution: Check batteries or switch to converter or change the wire set.

The wide variety and beauty of the natural materials used in vintage and antique jewellery is staggering. It seems jewellery designers never cease in their inventiveness. Here is a list which I believe is comprehensive or almost comprehensive (there is bound to be something I have left out).

I have excluded metal as that seems to deserve it’s own separate list.